Tank-type vacuum cleaners are capable of receiving dry materials, such as debris or dirt, as well as liquids. Such vacuum cleaners typically include an air impeller disposed inside an air impeller housing that is in fluid communication with an interior of the tank, thereby to create a low pressure area in the tank for vacuuming the dry and liquid materials. A motor is operatively coupled to the air impeller.
In all currently known wet/dry vacuum cleaners, the impeller must be shut off at some point in order to drain liquid from the tank. Some conventional vacuum cleaners have an enclosure in which the air impeller and motor are housed. The enclosure is removably attached to an upper, open end of the tank. To empty liquid from the tank, the impeller motor must be turned off and the enclosure removed from the tank before the tank may be tipped to dump liquid from the open end of the tank.
In other vacuum cleaners, the tank has an outlet drain formed near a bottom end of the tank that is closed off with a plug during vacuuming. When liquid is to be discharged from the tank, the plug is removed. The impeller motor must again be turned off to raise the pressure inside the tank, or else the liquid will not completely discharge from the tank.
It is also known to provide a pump with the vacuum cleaner for emptying the tank, such as in the vacuum cleaner described in commonly assigned U.S. Pat. No. 5,850,668. The pump and air impeller may be operated simultaneously, but the rate at which the impeller pulls liquid into the tank is typically higher than the rate at which the pump discharges liquid out of the tank. When the amount of liquid to be vacuumed is somewhat greater than the tank capacity, the tank ultimately becomes full. Consequently, the impeller and pump must be switched off for manual emptying of the tank or the vacuum cleaner must be operated without additional liquid entering the tank until the pump sufficiently empties the tank. Applications in which the volume of liquid to be vacuumed exceeds tank capacity include draining swimming pools or small ponds and removing water from flooded basements.